Ron, you forgot one thing that is bad about 15" wheels, and that is usually brake fitments. You can get a good sized brake, but you can usually get much larger with the bigger rims. Cooling might also be better as well since more of the rim can be opened. The big deal for me on the 15" is that they look good on a 60's car. Ever see an old muscle car with tires that are too low profile, not such a good thing (not always, but IMHO).
In any case might not make much difference for most people. The 15" tires are limited, I spent lots of time on the tirerack looking for 15" and the fronts are not a probem, but wide rears are (street tires). 17"s have much more selection, not huge, but good enough. From Hoosiers, Kumho's, Yoko's, etc most have some tire in the 295,315,335x17 size for the rears (Racing DOT tires). For street sizes just start poking around on the Tirerack, easy to see what is available and you can check out the spec's pages they have that will give all sorts of tire dimensions and fitment information.
I think the thread started in that you were looking at the Big lettered goodyears, one thing that I'm not sure of is if these are for street use how durable they would be vs. DOT approved style tires. I was warned from where I got them is that they should not be used on the street, and I thanked him for his obligatory reading of the legal disclaimers, and he said, yes, but they really should not be on the road as they are not built for the likes of road issues encountered. I'll have to carry a can of fix-a-flat I guess
Sandy